During recent years I have been investigating the auroral spectrum. 

 In the winter 1912 — 13 I undertook an expedition to Bossekop in Fin- 

 marken.' the main object of which was to study the auroral spectrum. With 

 a spectograph which combined a considerable dispersion with a great power 

 of light, I succeeded in photographing a few of the strongest lines in the 

 blue part of the auroral spectrum, and it was proved that these lines belong 

 to the so-called negative band spectrum of Nitrogen. 



During the winter 1921, I continued investigations in Christiania, and 

 here I made determinations of the green auroral line.- As the result of a 

 number of measurements, I found the auroral line to have the following 

 wave length: 



x = 5578.0 lint, units). 



Although the auroral line was determined with such an accuracy that 

 the error is only a fraction of an A unit, the origin of the line remains 

 as mysterious as ever. 



It was to be hoped that a more complete in\estigation of the whole 

 auroral spectrum might give us some valuable information also with regard 

 to the origin of the green line. But apart from this question, the deter- 

 mination of the auroral spectrum is a problem of the very greatest im- 

 portance, on account of its bearing on the question regarding the constitution 

 of the upper strata of the atmosphere and the nature of the cosmic electric 

 rays producing the aurora borealis. 



In the year 1921 the "Government Fund for Scientific Research" 

 furnished me with the necessary means for taking up this work in a more 

 systematic wa}-. A more complete description of experimental arrangements 

 will be given in a later work. Presently I shall only mention that during 

 the last winter (1922 — 23) three spectographs, which were put up last 

 summer, have been at work at the Geophysical Institute of Tronisö, where 

 the top roof of the building has kindly been put at my disposal by the 

 Director O. Krogness. — For the sake of convenience we shall give the 

 spectographs the following notation, viz. I, II and III (Roman numeral), 

 where : 



' L. Vegard : Phys. Z. S. 14, p. 677, 1913. Ann. d. Phys. 50, p. 853, 1916. Bericht 

 über eine Expedition nach Finmarken, Christiania Vid.-Selsk. Skr., Mat.-naturv. kl. 1916, 

 nr. 13. 



2 L. Vegard : Geofysiske Publikationer, Vol. II, Xo. 5. 



